The Treasury Department auctioned $30 billion in three-month bills at a discount rate of 0.055 percent, up from 0.040 percent last week. Another $25 billion in six-month bills was auctioned at a discount rate of 0.075 percent, unchanged from last week.

The three-month rate was the highest since these bills averaged 0.060 percent on June 24.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,998.61 while a six-month bill sold for $9,996.21. That would equal an annualized rate of 0.056 percent for the three-month bills and 0.076 percent for the six-month bills.

Separately, the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable rate mortgages, edged up to 0.12 percent last week from 0.11 percent the previous week.